1. Field of the Invention
This invention relates generally to a fingerprint image transmission system. More specifically, the invention relates to a fingerprint image transmission system for compressing and transmitting a fingerprint image from a remote computer system for sampling the fingerprint image to a central computer system recording the feature of the fingerprint in a database.
2. Description of the Related Art
In the related art, as image data compression system for transmitting an image data, there are a reversible or lossless coding (an information preserving or lossy coding) and a non-reversible coding (non-information preserving coding).
The reversible coding is a compression system which permits complete restoration of an original image. While the reversible coding achieves lower compression effect than the non-reversible coding, it is suitable for image transmission and accumulation when drop out of information is not permitted.
The non-reversible coding is a compression system for compressing an image data which sacrifices a part of information and thus is suitable for the case where high compression effect is given higher preference than complete restoration of the original image. As the reversible coding, there are a run length coding (Wyle coding, Huffman coding and so forth) disclosed in W. K. Pratt "Digital Image Processing", Wiley-lnterscience, 1978, a predictive coding disclosed in AT & T "Pattern Recognition Coding", CCITT SG VIII, Delayed Document, D124, 1982, an Elias coding disclosed in G. G. Langdon, Jr. and J. Rissanen, "Compression of Black-White Images with Arithmetic Coding", IEEE Trans. Vol. CON-29, No. 6, pp. 858-867, and Chain coding disclosed in H. Freeman, "Boundary Encoding and Processing" in Picture Processing and Psychopictories (B. S. Lipkin and A. Rosenfeld, eds.), Academic Press, 1970. On the other hand, as the non-reversible coding, there are a Discrete Cosine Transform disclosed in K. R. Rao and P. Yip, "Discrete Cosine Transform Algorithms, Advantages, Applications", Academic Press, 1990 and so forth.
In application of such image data compression systems to a fingerprint image transmission system, a compression factor cannot be made satisfactorily large to effectively reduce a data amount to be transmitted if solely the reversible coding is employed. Because of this, it takes a long time to transmit a thus compressed image. On the other hand, if the non-reversible coding is solely employed, the image before compression cannot be exactly reproduced without loss of data in a certain part.